My wife and I have put a good 50+ miles on our tandem in the one week we've had it.

There's one thing I would like to address which is the high speed gearing (is this the high or low gearing?). On the roads we ride, we are almost always on the lowest gearing and wish there can be a better ratio without increasing the comfortable cadence we're at. The bike has a 30/42/52t Truvativ Elita Crankset with a 9spd Ultegra cogset (12-27t) and 700C wheels. Is my best option to find a larger front chainring? If so..how large should I go? 55t? Where can I find these chainrings online and are they all compatible with the crankset I have? The bike is a Raleigh Coupe '05 if that helps.

Unless you are prepared to change all 3 rings, remember that the recommended maximum spread of teeth on the front derailler is 22t. This can be stretched to 24t, so if you stay with your 30--30+24= 54..
Some riders do manage to get a spread of more than 24t, but If you ask them, front gearchanges can be a bit hit and miss.

It is likely that in the long term you will be best served by learning to spin faster.

Presently, a better option might be to change the cassette for one with an 11T small cog. Keep in mind that it is possible to use parts of two cassettes to make up an 11-27, if that is what you must have.

How much extra gearing are we going to gain by going to a 11T vs the 12T cog. I don't have my cadence computer yet so I can't tell what kind of cadence we are maintaining...but I do not think only spinning faster will buy us what we are looking for. There is definitely room for a taller gear as we easily have the power to push the current setup and spin at a uncomfortable rate on level ground.

Also, since it's a tandem, wouldn't an 11T cog in the rear be quite stressful to the transmission? I would think a taller chainring will serve us better. Possible a 54 or 55t chainring.

I currently only know enough to be dangerous from browsing the web. I think what I'll be looking for is a 130bcd 54 or 55t chainring. Are they universally compatible across brands?

Give yourselves some time with the current setup.
You are suffering from 'new bike enthusiasm!' Boy, can we go fast on this thing! . . . but for how long? Give yourselves a thousasnd miles before thinking 'you gotto have these changes'.
How far do your ride? Sure, on short distances you can push a big gear. But can you push that 52x12 for 50+ miles in one session. 100 miles?
How about climbing hills? On long down hills, save your energy: tuck in and coast! You may coast down faster than what you can pedal!
Having said that, an 11T cog would be easier/cheaper than changing chainrings and possibly front shifter.

Thanks for the suggestions. I will definitely give the current setup some more time but anticipate that we will definitely make a change in the near future. We use our tandem more for daily exercising (10-25miles) rather than long rides. As it stands, each day we get out (like today) the faster we are riding and looking for another gear.

We are decently fit in our late 20's and about a 290lb team and want to get our heart rate up more.

So can I swap in pretty much any 54t or 55t chainring from any manufacturer? What are your opinions of FSA or Salsa as those seem to be the ones I can find.